(Chlamydmonas) living as haploid most of times produce diploid zygote and eventually it matures and turns into four haploids the fusion is initiated by extending actin fertilization tube -- actin is used by sea urchin producing both gametes
Unicellular eukaryote already has every basic concepts consist more complex organisms of other phyla.
(Vorvocaceans) living as haploid most of times, when sex is not needed asexual lifecycle -- two cell typesand gaining motality without death inducer(somatic regulator), somatic cells redifferentiate into gonidia, still being immortal. each gonidium cleavages into a small mold of its parent from noon to midnight inversion of gonidias into juveniles sexual reproduction once each year and resulting zygospore, separation of gametes in zygote production zygotes are produced to endure indefinite period of dry weather The stimulus for switching is known to be a 30000-Da sexual inducer protein.
From the story of Vorvox, we see that development is critically linked to the character of the ecosystem...